A better understanding of how neurobiological mechanisms influence social, emotional, and economic functioning among older adults could significantly improve quality of life in this population. The proposed research will involve both a cross-sectional and longitudinal component, and will test an integrative neurobiological model of the effects of aerobic exercise on social, emotional, and economic functioning, and the extent to which these effects are mediated by changes in functional network connectivity in the default mode and fronto-parietal control networks. The first specific aim of the study is to characterize age-related differences in network connectivity, and the relationship of these differences to executive functioning, and subsequent social, emotional, and economic functioning. The second specific aim is to examine whether a 6- month self-directed aerobic exercise intervention will attenuate age-related disruptions in brain network connectivity, executive functioning and consequently in social, emotional and economic functioning. A third exploratory aim will examine potential moderators of the effect of aerobic exercise on network connectivity. To accomplish these aims, we will collect data from 40 sedentary young adults (ages 25-35) and 265 sedentary older-adults (ages 65 or older). All participants will complete a battery of neurocognitive assessments including tests of executive function, psychosocial self-report measures, collateral (by a spouse or close relative) reports of social, emotional, and economic functioning, physiological measures of cardiovascular fitness (VO2 max test), and functional network connectivity via magnetic resonance imaging (MRI). Older adult participants will be randomly assigned to a 6-month aerobic exercise program or 6-month stretching and toning control program and be followed up at 3 months to track changes in psychosocial variables, as well as to receive a booster session to ensure proper adherence to the exercise prescription. Older adult participants will complete a second MRI scan and assessment of cardiovascular fitness (VO2 max test) at the final 6-month visit. At this time, these participants will complete te same battery of executive function, socio-emotional and economic functioning, and neurocognitive assessments completed at baseline. The proposed longitudinal and cross-sectional research on aerobic exercise, neurobiological mechanisms (e.g., functional connectivity and core executive functioning) and social, emotional, and economic functioning outcomes in older adults is expected to have significant clinical and scientific implications.